This invention relates to a toroidal coil motor in which toroidal coils are wound about an annular iron core to form a stator portion. A rotor portion with a magnet is rotatably provided in a central opening of the stator.
FIG. 1 shows a conventional toroidal coil motor. In FIG. 1, reference numeral 1 denotes an annular, iron core, reference numeral 2 denotes a n-pole, reference numeral 3 denotes a s-pole, reference numeral 4 denotes a rotation shaft, reference numerals 5 to 10 denote toroidal coils, reference numerals 11 to 13 denote laminate-fixing holes, and reference character R denotes a rotor portion.
FIG. 1 illustrates a top view as seen from the direction of the axis of the toroidal coil motor. The annular iron core 1 is formed by a plurality of silicon steel plates laminated in a direction perpendicular to the sheet of this Figure. The laminated plates are fixed together by passing laminate-fixing members respectively through the laminate-fixing holes 11 to 13. The laminate-fixing members are not shown in FIG. 1, for the ease of description.
FIG. 2 is a cross-sectional view in the vicinity of the line II--II of FIG. 1, that is, in the vicinity of the laminate-fixing member. In FIG. 2, the laminate-fixing member is designated 17. The silicon steel plates are designated 1-1.
After the silicon steel plates 1-1 are laminated together, the laminate-fixing member 17 is passed through the preformed laminate-fixing hole 11, and the laminated plates are fixed together, for example, by deforming the end of the laminating-fixing member 17.
Referring again to FIG. 1, the toroidal coils 5 to 10 are wound about the annular iron core 1 formed in the above-mentioned manner. In the example shown in FIG. 1, the number of the toroidal coils is six, but is not limited to six; however, each toroidal coil is designed to be connected to the toroidal coil spaced 180.degree. therefrom, and therefore the total number of the toroidal coils is always even.
The rotor portion R has a magnet having a required number of pairs of poles (In FIG. 1, one n-pole and one s-pole), and this rotor portion is rotatably provided in a central opening of the annular iron core 1.
In the toroidal coil motor of the above construction, the electric current flowing through the toroidal coils 5 to 10 is controlled by a signal from a magnetic pole position detection element 22, thereby producing an electromagnetic force rotating in a predetermined direction relative to the rotor portion R.
However, the above-mentioned conventional toroidal motor has a problem that the distribution of the magnetic flux in the annular iron core is not even or equal relative to the magnetic poles, so that the rotation is not effected smoothly (Microscopically, the rotational speed increases or decreases).
The above problem arises from the number and positions of the laminate-fixing holes.
Conventionally, the number and positions of the laminate-fixing holes 11 to 13 have been determined only depending on whether or not the number and positions are sufficient to fix the laminated silicon steel plates, without taking the number of the toroidal coils and the number of the magnetic poles of the rotor portion, R into consideration. As a result, in many cases, the traditional number of the laminate-fixing holes has been 3 or 4, and they have been positioned symmetrically.
With such an arrangement, the distribution of the magnetic flux in the annular iron core 1 is uneven relative to the magnetic poles of the rotor portion R, as described by the following. Arrows indicated by dotted lines in FIG. 1 show the paths of the magnetic flux produced by electric current flowing through the toroidal coils. Namely, the laminate-fixing holes 11 to 13 offer a greater magnetic resistance that the silicon steel plates 1-1 do, and therefore the path of the magnetic flux takes a great bend to avoid the laminate-fixing hole. On the other hand, at those portions of the laminate where no laminate-fixing hole is provided (for example, at that portion between the toroidal coils 5 and 6), the magnetic flux does not bend as described above, but flows in the circumferential direction.
A line B--B of FIG. 1 represents an extension line of the boundary between the n-pole 2 and the s-pole 3. When the rotational position of the rotor portion R is as in FIG. 1, that portion of the annular iron core 1 facing the n-pole 2 is disposed above the line B--B, and that portion of the annular iron core 1 facing the s-pole 3 is disposed below the line B--B.
When the magnetic flux distribution at that portion of the annular iron core 1 facing the n-pole 2 is compared with the magnetic flux distribution at that portion of the annular iron core 1 facing the s-pole 3, they are different from each other.
This discrepancy will now be described, taking one portion as an example. For example, note the portion of the annular iron core 1 disposed on the left side of the n-pole 2 in FIG. 1. This portion is an upper half of the portion of the annular iron core lying between the toroidal coils 9 and 10. The magnetic flux can pass through this portion in the circumferential direction without being disturbed by a laminate, fixing hole 11-13.
On the other hand, the portion of the annular iron core 1 facing the s-pole 3, a portion corresponding to the above-mentioned portion between toroidal coils 9 and 10 but disposed symmetrically therefrom across the rotational shaft 4, portion is the lower half of that portion lying between the toroidal coils 7 and 6. However, since the laminate-fixing hole 12 is provided in this portion, the magnetic flux takes a great bend to pass past this portion. Namely, the magnetic flux distribution is not even relative to the magnetic poles.
However, arrows are provided on both ends of a dotted line shown in drawing, since a direction of the magnetic flux distribution is changed in accordance with a direction of the electric current.